The present invention relates to a reflection mirror for a vehicle lamp and a method of forming the same in which the central luminous intensity is high and the rays of light are sufficiently diffused in the horizontal direction in the distribution of light used for a vehicle.
In the lamp including a reflection mirror, the shape of which is a paraboloid of revolution, and also including a front lens having lens steps arranged in front of the reflection mirror, it is difficult to make the front lens to be slanted. That is, it is difficult to make the front lens to put into a condition in which the front lens is greatly slanted on a vertical surface in accordance with the shape of a front nose of the vehicle. When the front lens is greatly slanted, the light distribution pattern is curved and the luminous intensity is reduced at both end portions in the transverse direction. In order to solve the above problems, the present applicant proposed a reflection mirror for a vehicle lamp, which is disclosed in U.S. Pat. No. 5,258,897, the summary of which is described below. The light distribution controlling function previously attained by a front lens is laid on the reflection mirror, and by utilizing the overall reflection surface of the reflection mirror, it is possible to form a light distribution pattern having a cut line peculiar to a low beam necessary for the light distribution of a vehicle lamp.
The reflection surface of this reflection mirror has a reference parabola which has been set on a horizontal surface containing the optical axis of the reflection mirror. Alternatively, the reflection surface of this reflection mirror has a reference parabola obtained when a parabola is projected on a horizontal surface containing the optical axis, the parabola being set on a surface rotated by a predetermined angle around the optical axis with respect to the horizontal surface containing the optical axis. A reference point is set on an axis passing through a top and a focus of the reference parabola, wherein the reference point is located on the same side as that of the focus with respect to the top, and a distance from the top to the reference point is longer than the focal distance of the reference parabola. Between the reference point and the focus, there is arranged a light source extending along the optical axis. The reflection surface has an optical axis parallel with a light vector of reflecting light obtained when light assumed to be emitted from the reference point is reflected at an arbitrary point on the reference curve, and the reflection surface is formed as a set of crossing lines obtained when an imaginary surface of paraboloid of revolution passing through the reflecting point, the focus of which is the reference point, is cut by a plane parallel with a vertical axis containing the light vector.
In this connection, in order to obtain a larger horizontal diffusion angle with respect to the above reflection mirror, it is considered to set the parabola, which is a reference curve, to be elliptical or hyperbolic.
FIGS. 41 to 44 are views showing a reflection surface "a" obtained in the following manner. An elliptical reference curve is set on a horizontal surface containing the optical axis. An enveloping surface is obtained by allotting a parabola extending in the vertical direction, to each point, wherein the parabola has an axis parallel with a direction vector of the reflecting light at each point on the reference curve. The thus obtained enveloping surface is a reflection surface "a". In this connection, in these views, a rectangular coordinate system is established, in which the optical axis is determined to be the x-axis, the horizontal axis perpendicular to the x-axis is determined to be the y-axis, and the vertical axis is determined to be the z-axis. The intersection O of these three axes is defined as an origin.
As shown in FIG. 41, a sectional curve "b" obtained when the reflection surface "a" is cut by the x-z plane is not symmetrical with respect to the x-axis. A curve b1 located on the upper side of the x-y plane is formed into a parabola, the focus F1 of which is located on the x-axis. In this case, the focal distance is denoted by f1. A curve b2 located on the lower side of the x-y plane is formed into a parabola, the focus F2 of which is located on the x-axis. In this case, the focal distance is denoted by f2, wherein f2&gt;f1. When a view of the reflection surface "a" is taken from the front, as shown by a solid line in FIG. 42, its outline is not circular, wherein a true circle is described by a broken line. As shown in the drawing, the outline of the reflection surface protrudes downward, that is, the outline of the reflection surface protrudes in the negative direction of the z-axis, and the width of the outline of the reflection surface is reduced in the direction of the y-axis.
In this connection, the filament "c", which is a light source, is assumed to have an ideal shape that is columnar. A central axis of the filament "c" is parallel with the x-axis, and the filament "c" is located between the focuses F1 and F2 under the condition that it comes into contact with the upside of the x-axis.
On the reflection surface "a", the reference curve "d" is set on the x-y plane. As shown in FIG. 43, the top of the reference curve "d" comes into contact with the y-axis at the origin O and is formed into an ellipse, one of the focuses of which is F1. Accordingly, on the assumption that a point light source is arranged at the focus F1, each ray of light emitted from the point light source is reflected on an arbitrary point P on the reference curve "d". Then, as shown by the characters "e", "e", . . . in the drawing, the rays of light are condensed at the other focus of the ellipse located on the x-axis. Then the rays of light cross the x-axis and diffuse in the horizontal direction.
FIG. 44 is a schematic illustration showing an arrangement tendency of the filament images projected on a screen disposed in front of the reflection surface "a" at a sufficiently long distance. In the drawing, the straight line H--H is a horizontal line corresponding to y-axis on the screen, and the straight line V--V is a vertical line corresponding to z-axis on the screen.
As can be seen in the above explanation, the filament images "g", "g", . . . projected on the screen by the regions on the reflection surface "a" on the left of the x-y plane when a view is taken from the front, are arranged under the line H--H on the left of the line V--V. The filament images "h", "h", . . . projected on the screen by the regions on the reflection surface "a" on the right of the x-y plane when a view is taken from the front, are arranged under the line H--H on the right of the line V--V.
In this connection, the closer to the x-axis the reflecting point on the reflection surface "a" is, the larger the projection area is, and the more distant from the x-axis the reflecting point on the reflection surface "a" is, that is, the closer to the periphery the reflecting point on the reflection surface "a" is, the smaller the projection area is. As shown by the rays of light "e", "e", . . . , the closer the ray of reflecting light is to the periphery on the reflection surface "a", the larger the angle of the ray of light with respect to a straight line parallel with the x-axis is increased. Due to the foregoing, the filament image of a small projection area is located at a position distant from the line V--V, and the filament image of a large projection area is located at a position close to the line V--V. In this connection, the filament images "i", "i", . . . , located along the line V--V are projection images formed by the points on the crossing line formed by the reflection surface "a" and the x-z plane.
As shown by the broken line in FIG. 44, a projection pattern obtained as a set of these filament images becomes slender as it separates from the line V--V, that is, the width of the projection pattern in the vertical direction is reduced as it separates from the line V--V.
FIGS. 45 to 48 are views showing a reflection surface "j" obtained in the following manner. An hyperbolic reference curve is set on a horizontal surface containing the optical axis. An enveloping surface is obtained by allotting a parabola extending in the vertical direction, to each point, wherein the parabola has an axis parallel with a direction vector of the reflecting light at each point on the reference curve. The thus obtained enveloping surface is the reflection surface "j". In this connection, in these views, a rectangular coordinate system is established, in which the optical axis is determined to be the x-axis, the horizontal axis perpendicular to the x-axis is determined to be the y-axis, and the vertical axis is determined to be the z-axis. The intersection 0 of these axes is defined as an origin.
As shown in FIG. 45, a sectional curve "k" obtained when the reflection surface "j" is cut by the x-z plane is not symmetrical with respect to the x-axis. A curve k1 located on the upper side of the x-y plane is formed into a parabola, the focus F1 of which is located on the x-axis. In this case, the focal distance is denoted by f1. A curve k2 located on the lower side of the x-y plane is formed into a parabola, the focus F2 of which is located on the x-axis. In this case, the focal distance is denoted by f2, wherein f2&gt;f1. When a view of the reflection surface "j" is taken from the front, as shown by a solid line in FIG. 46, its outline is not circular, wherein a true circle is described by a broken line. As shown in the drawing, the outline of the reflection surface protrudes downward, that is, the outline of the reflection surface protrudes in the negative direction of the z-axis, and the width of the outline of the reflection surface is increased in the direction of the y-axis.
The filament "c", which is a light source, is assumed to have an ideal shape that is columnar. A central axis of the filament "c" is parallel with the x-axis, and the filament "c" is located between the focuses F1 and F2 under the condition that it comes into contact with the upside of the x-axis.
On the reflection surface "j", the reference curve "l" is set on the x-y plane. As shown in FIG. 47, the top of the reference curve "l" comes into contact with the y-axis at the origin 0 and is formed into a hyperbola, the focus of which is F1. Accordingly, on the assumption that a point light source is arranged at the focus F1, each ray of light emitted from the point light source is reflected on an arbitrary point P on the reference curve "l". Then, as shown by the characters "m", "m", . . . in the drawing, the rays of light are gradually separated from the x-axis as they come to the front, that is, as they come in the positive direction of the x-axis, they are diffused in the horizontal direction.
FIG. 48 is a schematic illustration showing an arrangement tendency of the filament images projected on a screen disposed in front of the reflection surface "j" at a sufficiently long distance. In the drawing, the straight line H--H is a horizontal line corresponding to the y-axis on the screen, and the straight line V--V is a vertical line corresponding to the z-axis on the screen.
As can be seen in the above explanation, the filament images "n", "n", . . . projected on the screen by the regions on the reflection surface "j" on the left of the x-y plane when a view is taken from the front, are arranged under the line H--H on the right of the line V--V. The filament images "o", "o", . . . projected on the screen by the regions on the reflection surface "j" on the right of the x-y plane when a view is taken from the front, are arranged under the line H--H on the left of the line V--V.
The closer to the x-axis the reflecting point on the reflection surface "j" is, the larger the projection area is, and the more distant from the x-axis the reflecting point on the reflection surface "j" is, that is, the closer to the periphery the reflecting point on the reflection surface "j" is, the smaller the projection area is. As shown by the rays of light "m", "m", . . . , the closer to the periphery on the reflection surface "j" the ray of reflecting light is, the larger the angle of the ray of light with respect to a straight line parallel with the x-axis is. Due to the foregoing, the filament image of a small projection area is located at a position distant from the line V--V, and the filament image of a large projection area is located at a position close to the line V--V. The filament images "p", "p", . . . located along the line V--V in the vertical direction are images projected from the points on the crossing line formed by the reflection surface "j" and the x-z plane.
As shown by the broken line in FIG. 48, a projection pattern obtained as a set of these filament images becomes slender as it separates from the line V--V, that is, the width of the projection pattern in the vertical direction is reduced as it separates from the line V--V.
In the reflection mirror having the above reflection surface, the following problems may be encountered. It is difficult to ensure both a predetermined central luminous intensity and a diffusion of rays of light in the horizontal direction under the condition that the rays of light have a sufficient width in the vertical direction.
Specifically, in the above reflection surface on which the reference curve is formed to be elliptical or hyperbolic, the following problems may be encountered.
(1) A small filament image projected by the periphery of the reflection surface extends in the horizontal direction.
As explained before with reference to FIGS. 44 and 48, concerning the filament image projected at a position close to the periphery of the reflection surface, the more the filament image is diffused in the horizontal direction, the smaller the projection area will become. Therefore, when the end portions of the projection pattern in the transverse direction are separated from the line V--V in the horizontal direction, the projection pattern becomes slender, so that the visibility is lowered in the periphery.
(2) When an insertion hole to insert the light source is formed on the reflection surface, a luminous intensity at the center of the light distribution pattern is insufficient, that is, a luminous intensity in the hot zone is insufficient.
An insertion hole into which an electric bulb is inserted is formed on the reflection surface at a position close to the intersection where the reflection surface crosses the x-axis. Therefore, in the region AR on the reflection surface shown in FIGS. 41 to 43 or FIGS. 45 to 47, rays of light are not reflected. As a result, an image, the projection area of which is large, is missing as shown by the filament images "i", "i" . . . in FIG. 44 or the filament images "p", "p", . . . in FIG. 48.
An upper end portion of the filament image "i" or "p" contributes to the formation of the central luminous intensity portion. Accordingly, if the upper end portion of the filament image "i" or "p" is missing, the luminous intensity is directly lowered. Unless the filament image, which contributes to the formation of the central luminous intensity portion, is made up by some means for operating the curved surface so that the missing portion can be compensated by other portions, or unless the filament image is made up by the action of lens steps provided on the front lens, it is difficult to sufficiently ensure the luminous intensity of the portion circled by the two-dotted chain line in FIG. 44 or 48.